Simplifying documentation and shared responsibility documentation

[choldgraf]

This refactors and simplifies our service documentation with a few major goals:

• Reduce the total number of pages that users click through
• Make our Shared Responsibility Model more well-described
• Move some of the strategic and policy documentation to our Team Compass (because even I had forgotten it was in here)
• Reduce duplicated and redundant information and instead link to a single source of truth

Still WIP but posting here as a first step in case there is feedback.

To Do

• Flesh out the Shared Responsibility Model section

References

• ref: Make our Shared Responsibility Model more granular and link it to what kind of support we offer #173
• sibling to: Move strategy docs here from service team-compass#572

[yuvipanda]

This has been open long enough, let's merge this. Thanks @choldgraf